Federals agents this morning raided and detained about 300 people they believe to be illegal aliens working at House of Raeford's Columbia Farms poultry plant in Greenville -- an operation that one immigration official today called the biggest workplace raid ever in the Carolinas.

Investigators expected to spend the rest of Tuesday at the plant poring over employment documents and conducting interviews to gather evidence in what U.S. Attorney Walt Wilkins said will be an ongoing investigation into House of Raeford's employment practices.

Several workers began running for the doors as agents raided the processing plant at about 8:50 a.m. this morning as shifts were changing, witnesses said. All told, 450 officers were involved in the raid, though not all actually entered the building, Wilkins said.

The raid marks the biggest move yet in a 10-month federal investigation into hiring practices at the processing plant. In recent weeks, seven supervisors at the plant have pleaded guilty to falsifying employment documents . A human resources manager faces 20 counts of felony immigration fraud.

The raid is the biggest ever in the Carolinas, said Ken Smith, special agent-in-charge of the Atlanta Immigration and Customs Enforcement investigations office.

In the course of the investigation, agents reviewed 825 "I-9 forms" that verify a worker's immigration status -- and of those, 94 percent were found to be falsified, Wilkins said.

Of the 300 detained today, 58 have been let go and will be monitored as part of a "humanitarian detention program that will allow for hardships such as dependent children and medical issues, Wilkins said.

Workers inside the plant at the time of the raid said that several workers started running for the doors about 8:50 a.m.

"I had to duck back into the bathroom to keep from getting trampled," janitor Herbert Oscar Rooker said.

Nicole Freeman said she was putting a chicken breast on a machine when the running began. Some of the workers were yelling, "Policia!" and "ICE!" she said.

Agents blocked the doors, and workers were directed into a break room, Freeman said.

All U.S. citizens were told to go to one side of the room, while non-citizens were directed to the other side, Freeman said. She estimated the crowd at about 300.

Workers had to write down their names, where they were born and their parents’ names, Freeman said.

"They made us show our ID," she said.

Workers who were allowed to leave had to put on blue wristbands bearing their names to get out the door, Freeman said.

While about 450 agents were involved in today’s operation, not all of them were on the scene, Wilkins said.

Truck driver Richard Worley said he was going to pick up his trailer when he saw "about 100" agents swarm the plant. From the outside of the plant, he couldn’t see workers running, he said.

"It’s just wild," Worley said.

Wilkins said the majority of illegal workers will be administratively processed and deported. The U.S. Attorney’s Office will handle any cases deemed worthy of prosecution, he said.

In the raid’s aftermath, friends and family gathered outside the Columbia Farms’ gate to await word on their loved ones.

Three small children ran around a tree and kicked rocks. A woman wiped away tears.

Melissa Islas of Greenville waited to learn about her friend, who she said was a single father of a 17-month-old boy named Anthony.

"If I have to, I’ll take care of him," she said.

Some workers were confused about when they were supposed to return to the plant.

"I came out here because the officer told me to go home," supervisor Luis Mahecha said.

But Mahecha said he saw his boss outside, and he said, "Don’t go. We’re trying to work later on."